1. Field of the Invention
This invention relates to a pressure relief valve for brake pressure pipes in railway brake emergency systems, and more particularly an improved self-cleaning diaphragm valve of the type that is actuated by a solenoid-operated pilot valve.
Solenoid-operated diaphragm valves are used as emergency brake control valves in emergency brake systems. In a railway train each vehicle is fitted with a brake pipe extending along the length of the vehicle. The brake pipes of each vehicle of a train are interconnected to each other to form a continuous brake pipe extending from the locomotive to the last vehicle. The continuous brake pipe provides pressurized air to each vehicle, causing the pistons in the brake cylinders at each car to be withdrawn to effect a full brake release. In case of an emergency, the pressure in the brake pipe is lowered quickly to actuate the pistons, thereupon causing brake action.
A number of things can block the brake pipe. Water can collect and freeze in the low lying glad-hand joints. Each car has brake pipe valves that can rotate shut. If the brake pipe is, for example, blocked in the middle of the train and air is bled through a valve situated at the front of the train, the drop of pressure in the rear part of the brake pipe, i.e. behind the block, may not be sufficient to actuate the brake pistons.
For this reason, brake emergency control valves that can be remotely actuated are situated at the end of the brake pipe to enable the locomotive engineer to relieve pressure from the rear end of the brake pipe as well as the front end, thereby assuring fast function of emergency braking system.
However the dirt and debris in the brake pipe can interfere with the proper function of prior art emergency brake pressure relief valves situated at the end of the train.